About the Flu and T1D

Tis the season…

To get your flu shot!

Last year set a record for length of flu season, which lasted a remarkable 21 weeks according to the CDC.  While severity was rated as moderate last year, getting the flu is never fun.  Some may enjoy staying home from work/school, but rarely has anyone wished the flu upon themselves.  Luckily, you can take steps to help protect yourself, and the best way to protect against getting the flu is to get your yearly flu shot!

There’s been a lot of talk about the flu shot these days, and as a person with type 1 diabetes I’ve always wondered about my susceptibility to infection with flu and how best to avoid getting the flu.

What is the flu?

The Flu is a contagious respiratory illness which is caused by influenza viruses.  Influenza viruses can infect the nose, throat, and sometimes the lungs.  People who are infected with the flu often feel some of the following symptoms: fever, cough, sore throat, runny nose, muscle aches, fatigue, and sometimes vomiting/diarrhea.

Influenza viruses belong to the Orthomyxoviridae family and possess a segmented single stranded RNA genome.  There are three types of viruses categorized based upon genetic and antigenetic differences that cause flu: Influenza A, B, and C. 

Influenza A

Generally, Influenza A is thought to account for approximately 2/3 of human infections each year, and has been the type responsible for most worldwide flu pandemics.  There are many subtypes of Influenza A which are determined by two viral proteins: hemagglutinin (HA/H) and nueraminidase (NA/N).  H1N1, H1N2, and H3N2 have all been found circulating in humans.

Influenza B

Influenza B tends to cause milder disease than influenza A.  Currently circulating influenza B viruses belong to the B/Yamagata or B/Victoria lineages (referring to the location where it was first isolated).

Influenza C

Influenza C is not often discussed as infection is generally mild or subclinical.

What is the Flu Shot?

The flu shot is a vaccine administered primarily intramuscularly (into the muscle, often the arm).  The vaccine contains inactivated or attenuated (weakened) viruses that cause the body to develop antibodies against the strains of the virus included in the vaccine approximately two weeks after vaccination.  This allows your immune system to recognize and fight off the virus if it comes into contact with it in the future.

Most vaccines in the United States are quadrivalent, protecting against two influenza viruses (H1N1 and H3N2) and two influenza B viruses (Victoria Lineage and Yamagata lineage).    If you’re curious, this years vaccine contains an A/Brisbane/02/2018 (H1N1)pdm09–like virus, an A/Kansas/14/2017 (H3N2)–like virus, and a B/Colorado/06/2017–like virus (Victoria lineage), and aa B/Phuket/3073/2013–like virus (Yamagata lineage).   The trivalent influenza vaccine contains the two influenza A strains (H1N1 and H3N2) and one influenza B virus (Victoria).  

Every year, the CDC characterizes about 2,000 influenza viruses, and compares them to the viruses that were included in the vaccine, and to monitor for changes in the virus.  This is then utilized to determine which viruses to include in the next years influenza vaccine. 

While efficacy of the vaccine varies from year to year, the vaccine is typically 30-60% effective against the flu.  Influenza viruses are constantly changing and evolving through a process called antigenic drift.  Even when viruses differ somewhat from the vaccine, it is thought that the vaccine may still provide some protective benefits.   

While the vaccine is not perfect, it’s clearly the best way to protect yourself against the flu.  There are actually multiple vaccine options, so check out the CDC website for more info.

The Flu and T1D

While not all studies show an increased risk of influenza among people with type 1 diabetes, there are a few studies suggesting that influenza severity may be increased in people with diabetes.  

There is a growing body of evidence suggesting that chronic hyperglycemia may impact immune function and possibly viral replication; however, few studies have looked at susceptibility to influenza infection specifically in type 1 diabetes.

That being said there is quite a bit of research supporting the safety and efficacy of the flu vaccine in people with diabetes.  One study suggested that the flu vaccine reduced hospital admissions related to influenza by as much as 79%.  The CDC recommends the flu shot for people with diabetes.  

If you do get the Flu

The flu can make it challenging to keep your blood sugars in range, as the body often produces stress hormones during illness that raise blood glucose.  It may be necessary to contact your physician about adjusting your insulin if your blood sugars are out of range.  People with type 1 diabetes are often at an increased risk of diabetic ketoacidosis (DKA) during illness, so it may be necessary to test ketones regularly.

No one wants to get the flu, so get your flu shot early!

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